Film processing methods and apparatus have been available for a number of years. However, it is not believed that the methods previously utilized for standard polymeric films, can readily be employed in the formation of thermotropic polymer films, especially films having the unique characteristics of those prepared herein.
For example, U.S. Pat. No. 4,370,293 to Petersen-Hoj describes a method and apparatus for the manufacture of biaxially oriented plastic films, particularly polyester films. The process described for polyester comprises extruding polyester through an annular die to form a seamless tube and inflating the tube by means of a pressurized gas. The expanded tube thus formed is drawn out in a longitudinal direction, cooled and flattened. The flattened tube is heated to the orientation temperature of the film, expanded again, and stretched in its longitudinal direction. These stretching techniques are said to impart a biaxial orientation to the polymeric backbone of the film.
Similarly, U.S. Pat. No. 4,011,128 to Suzuki describes a method and apparatus for forming a cross-oriented film, wherein a non-oriented film to be treated is first formed by conventional methods, then cross-oriented by stretching and twisting. In addition the cross-oriented film is flattened so as to continuously form a laminated cross-oriented film.
U.S. Pat. No. 4,358,330 to Aronovici describes a method and apparatus for manufacturing films having pairs of adjacent layers whose molecular orientation is in different directions. The method employed is a modification of the conventional "blown film" technique such that the molecular chains forming the layers of film are oriented substantially immediately prior to their solidifying.
U.S. Pat. No. 4,496,413 to Sharps, Jr., describes a process and apparatus for the preparation of a blocked cross-plied polymer film which involves the extrusion of a polymer melt through a tubular rotary die. The rotation of a single member of the die is said to impart a molecular orientation to the polymer in a transverse direction during the extrusion. The film is blocked by expanding the film and then pressing opposing walls together to produce a composite film having at least two layers, each having a transverse molecular orientation opposing the other. The composite film is said to have a balanced cross-ply.
The disclosures of each of the above described patents are incorporated herein by reference.